United States
Environmental Protection
Agency
EPA/540/SR-94/512
May 1994
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Emerging Technology
Summary
Cross-Flow Pervaporation for
Removal of VOCs from
Contaminated Wastewater
Pervaporation is a membrane tech-
nology using & dense, nonporous poly-
meric film to separate contaminated
water from a vacuum source. The mem-
brane preferentially partitions the vola-
tile organic compounds (VOC) organic
phase used In this test This process
has proven to be an alternative to con-
ventional technologies because it re-
moves VOCs without requiring any pre-
or post-treatments and Is cost-effec-
tive.
This Summary was developed by
EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the SITE Emerging Tech-
nology program that are fully docu-
mented In a separate report (see
ordering Information at back).
Background
Water contaminated with VOCs is en-
countered throughout industry and in many
groundwater and site remediation situa-
tions. VOCs are common contaminants
found in groundwater, leachate, and waste-
water. Approximately 50% of the U.S. En-
vironmental Protection Agency's (EPA's)
list of priority pollutants is composed of
VOCs—compounds known to be toxic, or
carcinogenic, or both.
Conventional technologies such as air
stripping and activated carbon treatment
are the current methods used to remove
low concentrations of organic contaminants
from various water sources. Previous work
has demonstrated that pervaporation is a
potentially suitable remediation method for
Wastewater applications. The primary ob-
jectives of this project were to develop an
improved membrane and module design
to make pervaporation a more cost-effec-
tive method for removing VOCs from con-
taminated water and to compare the
improved pervaporation module and mem-
brane design with conventional remediation
technologies as well as other pervaporation
module and membrane designs:
Technology Description
Pervaporation is a membrane process
for removing VOCs from wastewater,
leachate, and contaminated groundwater
(Figure 1). For water treatment applica-
tions, the membrane is made of an
organophilic polymer such as modified sili-
cone rubber, which exhibits high selectiv-
ity for organic compounds while allowing
very little passage of water. Only the mi-
nor component (organic compounds) of
the feed goes through the membrane,
which reduces the potential for membrane
fouling. One side of the membrane is in
Printed on Recycled Paper
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Pervaporation module
Treated effluent
Aqueous waste
Feedpump
Permeate
Vacuum pump
Organic liquid
FJgun 1. Schematic of pervaporation process for removing VOCs from wastewater.
contact with the VOC-contaminated wa-
ter; the other side is exposed to a vacuum.
VOCs are absorbed in the membrane and
diffuse through to the other side where
they are drawn off by vacuum. The treated
water is depleted of VOCs and exits the
pervaporation system for collection or dis-
charge. VOCs passing through the mem-
brane, now called permeate, are
condensed and flow to a permeate collec-
tion tank where gravity separation of wa-
ter and VOCs occurs. The VOC phase is
pumped from the base of the collection
tank to storage. Collected water is re-
turned to the pervaporation system for
further treatment.
Project Accomplishments
During the project, membranes and
modules were developed, and several
module cartridges were produced to evalu-
ate their performance. Testing was car-
ried out at bench scale with separate
synthetic wastewaters containing trichlo-
roethytene (TCE), toluene, or ethylene
dfchforide. These components vary sig-
nificantly in volatility (as defined by Henry's
Law Constant) and other secondary prop-
erties. To Identify key operating param-
eters, these components were tested at
various temperatures and vacuum pres-
sures. Bench testing was followed with
pilot testing. A 5-ft2 membrane area was
used to treat water contaminated with tolu-
ene. Testing whh the 5-ft2 module verified
the results of the bench testing. A com-
puter model, developed from the bench-
test results, was used to predict and
optimize pervaporation conditions for ef-
fective removal of VOCs from wastewa-
ter.
Results To Date
The results of this project have shown
that pervaporation performance depended
greatly on both the membrane and mod-
ule design. The module, composed of hol-
low fibers, was designed to allow liquid to
flow orthogonal to the fiber direction. This
high mass transfer allowed the membrane
surface area requirements to be minimized.
The effective combination of membrane
and module allowed the waste VOC to be
concentrated by 5,000 to 50,000 times as
it was removed from the wastewater. The
permeate always separated into an aque-
ous and organic phase. In practice, this
would offer the possibility of recovering
the organic fraction for industrial applica-
tions.
Pervapbratibn performance for VOC re-
moval depends on (1) VOC type, (2) mem-
brane type, (3) liquid turbulence in the
module, (4) operating temperature, and
(5) vacuum pressure. Pervaporation per-
formance is optimal for VOCs with a solu-
bility of less than 1%. High solubility VOCs,
such as ethyl acetate, methylene chloride,
and ethylene dichloride can, however, be
considered but require higher operating
temperatures to enhance VOC removal.
Higher operating temperatures marginally
increase operating costs. Membranes
should be organophilic to minimize water
passage. In this study, a modified silicons
rubber membrane was used, and the
pervaporation module demonstrated mass
transfer coefficients above 100 u,m/s. This
represents a performance enhancement
of 2 to 4 times ithat of previous work.
Furthermore, this enhancement reduces
the membrane area requirement by 2 to 4
times for any given application. Membrane
thickness and type reduce the passage of
water and, thereby, increase separation
factors. This reduces operating costs sig-
nificantly. Operating temperature and
vacuum pressure are interrelated. Since
the ultimate vacuum pressure depends on
the condenser temperature (minimum 0°C)
and the VOC present in the condenser,
the operating temperature of the feed must
be sufficient (typically greater than 60°C)
to provide a vapor pressure gradient
(chemical potential) from the membrane
to the condenser, j
Pervaporation also has the following
advantages over: conventional technolo-
gies: I
• No chemicals or air is added to the
wastewater,'therefore fouling and
scaling problems are avoided.
• Pervaporation does not require
sorbents or chemicals.
• Monitoring for breakthrough is not
required. j
• Recovered solvents may be reused
in industrial applications.
• Degree of VOC removal is
independent of concentration and type
of VOC. I
A cost comparison of pervaporation with
conventional technologies was conducted
for a 44-gpm application with 10 ppm TCE
to be reduced to 0.1 ppm TCE. Cost analy-
sis indicates that peryaporatipn was more
cost-effective than air stripping and acti-
vated carbon. i
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Field testing through the SITE program
will be carried out through 1994 to verify
these pervaporation results.
The full report was submitted in fulfill-
ment of cooperative agreement CR-
815788 by the Wastewater Technology
Center and Zenon Environmental Inc. un-
der the sponsorship of the U.S. Environ-
mental Protection Agency.
•ft-U.S. GOVERNMENT PRINTING OFFICE: 19*4 - S50-O67/80257
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The EPA Project Manager, John Martin, is with the Risk Reduction Engineer-
ing Laboratory, Cincinnati, OH 45268 (see below).
The complete report, entitled "Cross-Flow Pervaporation System for Removal
of VOCs from Contaminated Wastewater,"(Order No. PB94-170230; Cost:
$19.50, subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA221'61
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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